Troubleshooting

No communication via UART

If no data is being transferred between the host system and the module, the following causes are possible:

Voltage levels incompatible:

The module operates at 3.3 V logic levels. Make sure that the host system's UART interface is also 3.3 V compatible. Direct connection to 5 V UART levels can damage the module.

Check UART configuration:

Make sure that the interface is initialized correctly. The default configuration is:

• Baud rate: 115200
• Data bits: 8
• Stop bits: 1
• Parity: none
• Flow control: none

No data visible in the cloud

If the device is connected correctly but no data appears in the cloud interface, the following steps help narrow down the cause:

Check UART protocol:

Is the message being sent in accordance with the UART protocol specification? Ensure that the frame format is correct (start byte, length, payload, CRC). The module acknowledges valid messages with a response – if this is missing, the cause is often a protocol error.

Check device status in the cloud:

Open the Coldwave cloud and check the status of the device. A device may, for example, be marked as "offline" if:

• no valid cellular connection is available (internal error)
• the cloud blocks the device due to configuration errors
• the last message was invalid and could not be processed

LED codes for status indication

The module has 3 status LEDs that signal different operating states:

Color / blink pattern	Meaning
Green continuously on	Normal operation, cloud connected
Green flashing rapidly	Connection to the cloud in progress
Green flashing slowly	Data synchronization with the cloud
Red flashing twice in succession	No connection to the cloud possible (network error)
Red flashing three times in succession	No connection to the cellular network
Red flashing four times in succession	SIM card faulty/locked
Yellow (all states)	Cellular network data indicator

Behavior in case of invalid UART messages

The YUKI Module A1 is robust against invalid input: Invalid or incomplete messages are discarded internally and do not trigger any reaction. No feedback is sent via UART.

In case of repeated protocol errors or an "out-of-sync" condition, it is recommended to perform a targeted reset of the module via the RESET pin.

The module contains an internal watchdog that automatically triggers a restart in the event of serious internal errors.